The spider Gaelnath has stolen an ancient dwarf-make rune-stone.
'Troubles abound in Ered Luin, but this not the least. Rumours abound of an ancient spider, Gaelnath, that has come into the possession of a particularly important dwarf-make rune-stone.
'If you are up to the challenge, head back into the Foundations of Stone and look for Tunzelgund along the northern edge of its central region. To the north of Tunzelgund you will find Gaelnath.
'I want you to get this rune-stone and take it back to Márus. He will know what to do with it.'
Gaelnath should be found in the Foundations of Stone, far to the east of Thorin's Hall.
Dwalin told you to recover the dwarf-make rune-stone from the spider Gaelnath and bring it to Márus.